1. Field of the Invention
This invention relates generally to polymer metal hybrid (PMH) technology, and more particularly to forming plastic features on metallic substrates.
2. Description of the Background Art
Polymer metal hybrid (PMH) technologies are currently being used to manufacture a wide variety of parts such as, for example, electronic device enclosures, automotive instrument panels, etc. In general, PMH technology refers to the various known techniques of bonding polymers to metal. Some of the more common applications that employ PMH techniques involve forming plastic features (e.g., mounting bosses, snap fits, reinforcement ribs, etc.) directly on metal surfaces such that the end product is a single part integrally formed from both metal and plastic features. For example, cellular phone housings often include a plurality of plastic mounting features (e.g., screw boss, snap-fits, etc.) molded directly on the interior surface of a thin metal shell. PMH technology can potentially provide several advantages over traditional all-metal/all-plastic parts including lowering manufacturing costs, lowering number of components in the overall hosting device, size/weight reduction, providing more design freedom, etc. Although such advantages are desirable to manufacturers, conventional PMH technologies typically cannot achieve very high plastic-to-metal bond strengths and are, therefore, only practical in a select few applications. As a result, continued research and development efforts focus on improving the plastic-to-metal bond strengths in PMH technologies. It is predicted that more and more all-metal/all-plastic parts will be replaced by PMH parts as bonding strengths continue improve. Therefore, it would be desirable to develop PMH techniques with improved polymer-to-metal bonding strengths.
Currently, plastic features can be formed on metal surfaces using several known variations of PMH technology such as, for example, nano-molding technology (NMT), metal adhesive molding (MAM) technology, aluminum non-adhesive molding (ANM), polymer injection forming, etc.
Forming plastic features on metal parts via NMT involves multiple steps that are summarized as follows. First, the bare metal part undergoes a multi-stage pretreatment process to remove unwanted grease, oil, oxides, etc. This involves subjecting the metal part to multiple chemicals baths including degreasing agents, acid solutions, base solutions, etc. After the multi-stage pretreatment process, the metal part is submerged in a T-solution. Then, the treated metal part is rinsed in diluted water. Finally, the metal part is inserted into a mold wherein resin is injected and formed directly on the treated surface.
Although NMT may be suitable for some applications, it has some shortcoming. For example, NMT requires a tedious multi-stage pretreatment process. As another example, the overall NMT process requires the use of hazardous chemicals. As yet another example, the polymer-to-metal bond achieved via NMT has a relatively short shelf-life, with the adhesion strength diminishing after several weeks of storage. Therefore, NMT is not practical for many applications.
What is needed, therefore, is a simpler system and method for manufacturing PMH parts. What is also needed is a system and method for manufacturing PMH parts that can achieve higher polymer-to-metal bonding strengths. What is also needed is a system and method for manufacturing PMH parts using less hazardous materials.